What Causes the ABS Yellow Light to Illuminate?

[JaylaFitz]

There are multiple states of the ABS warning light, each with different causes and solutions: State 1: ABS warning light remains constantly illuminated (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by dirt, mud, or other contaminants, affecting its ability to detect wheel speed signals. This prevents the ABS control module from determining vehicle speed or wheel slip rate, thus failing to issue appropriate braking commands. Solution: Clean the wheel speed sensor and adjust the gap between the sensor and the tone ring. Cause 2: Loose wiring connections or poor contact in ABS relays causing signal issues. Solution: Inspect and reconnect any loose wiring connections. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: Battery voltage drops below 10.5V when multiple electrical components are in use. The light extinguishes when engine RPM increases and voltage rises. Possible low voltage supply to ABS system due to poor connections. Solution: Check battery specific gravity, charging system, and power supply connections (voltage relay or power contacts). State 3: ABS warning light stays on after engine start until engine is turned off. Cause: Poor ground connection at ABS hydraulic valve body; faulty wiring connections; ABS control module failure. Solution: Loosen and retighten hydraulic valve body ground screw (clean contact surface if necessary); check connector gaps; replace ABS or ABS/ASR control module. State 4: ABS warning light illuminates during high-speed driving. Cause: ABS control module detects significant speed difference between front and rear wheels; incorrect tire or wheel specifications. Solution: Verify correct tire and wheel specifications (refer to fuel filler door sticker). State 5: ABS warning light flashes intermittently. Cause: Improper brake light switch adjustment; internal contact issues in brake lights. Solution: With engine running, depress brake pedal and manually push brake switch linkage downward to reset position; replace brake light switch if needed. When the ABS warning light is on, continued driving is not recommended. ABS malfunction means loss of anti-lock braking function - locked wheels during emergency braking may cause skidding and loss of vehicle control, creating significant safety hazards.